... but you could swap the dictionaries used (if you use Hunspell) so that Studio reads en(UK) to match your existing project but uses the contents of the en(US). Or you could export to word using the SDLXLIFF Converter and spell check in Word using a US dictionary.
To do the Hunspell method go to here (I've assumed a 64-bit machine but remove the (x86) part if not):
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